Image forming apparatus with mode for setting transfer voltage

ABSTRACT

An image forming apparatus includes an image bearing member; a transfer member configured to transfer a toner image carried on the image bearing member to a sheet by being applied with a voltage; a controller configured to execute a mode of outputting a test chart for setting a voltage to be applied to the transfer member during image formation, the mode being a mode of transferring a plurality of test images to the test chart by applying a plurality of different voltages to the transfer member; and an operation portion capable of setting a type of a sheet on which the mode is executed. The controller is configured to preset a voltage value for setting a voltage to be applied when the test images are transferred in execution of the mode based on a voltage value, which is set in the previous execution of the mode.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to an image forming apparatus such as an electrophotographic copying machine and an electrophotographic printer (for example, a laser beam printer, an LED printer, etc.).

Description of the Related Art

A configuration of an electrophotographic system image forming apparatus is widely known in which a full-color toner image formed by superposing yellow, magenta, cyan, and black toner images is transferred to a sheet by applying a voltage to a transfer member to form an image.

Japanese Patent Laid-Open No. 2000-221803 describes a configuration in which such an image forming apparatus executes a mode of adjusting a transfer voltage to be applied to a transfer member. In this mode, the transfer voltage to be applied to the transfer member is switched to form a plurality of patch images on the sheet, and the user checks the transferability of the patch images and sets an optimum transfer voltage.

Japanese Patent Laid-Open No. 2004-280003 describes a configuration in which a transfer voltage serving as a reference for forming a patch image can be set by a user in a mode of adjusting the transfer voltage.

However, in the configuration described in Japanese Patent Laid-Open No. 2004-280003, in order to use a result of the mode executed in the past when setting the transfer voltage as the reference for forming the patch image, the result of the mode needs to be recalled by a call button, which is troublesome for a user.

SUMMARY OF THE INVENTION

It is desirable to provide an image forming apparatus that can easily use a result of a mode in the past in a mode of adjusting a transfer voltage.

A representative configuration of the present invention is is directed to an image forming apparatus that includes an image bearing member; a transfer member configured to transfer a toner image carried on the image bearing member to a sheet by being applied with a voltage; a controller configured to execute a mode of outputting a test chart for setting a voltage to be applied to the transfer member during image formation, the mode being a mode of transferring a plurality of test images to the test chart by applying a plurality of different voltages to the transfer member; and an operation portion capable of setting a type of a sheet on which the mode is executed, wherein the controller is configured to preset a voltage value for setting a voltage to be applied when the test images are transferred in the mode based on a voltage value, which is set in the previous mode.

Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of an image forming apparatus;

FIG. 2 is a block diagram illustrating a part of a system configuration of the image forming apparatus;

FIG. 3 is a flowchart of a setting mode;

FIG. 4A and FIG. 4B are diagrams each illustrating a display screen of an operation portion;

FIG. 5A and FIG. 5B are diagrams each illustrating a state in which a patch image is formed on a sheet;

FIG. 6 is a schematic cross-sectional view of an image forming apparatus;

FIG. 7 is a schematic diagram of a spectroscopic sensor;

FIG. 8A and FIG. 8B are diagrams each illustrating a status A filter and visual spectral characteristics; and

FIG. 9 is a flowchart of a setting mode.

DESCRIPTION OF THE EMBODIMENTS First Embodiment

<Image Forming Apparatus>

First, the overall configuration of the image forming apparatus according to the first embodiment of the present invention will be described with reference to the drawings together with an operation during image formation. Note that the dimensions, materials, shapes, and relative arrangements of the described components are not intended to limit the scope of the present invention only to those unless otherwise specified.

The image forming apparatus A transfers yellow Y, magenta M, cyan C, and black K toners to an intermediate transfer belt, and then transfers images to a sheet to form an image. Note that, in the following description, the members that use the toners of the above-described respective colors are associated with letters Y, M, C, and K, but the configuration and operation of each member are substantially the same except that the colors of the toner to be used are different from each other. Therefore, these letters are omitted as appropriate unless distinction is required.

As illustrated in FIG. 1, the image forming apparatus A includes an image forming portion 40 configured to transfer a toner image onto a sheet S to form an image, a sheet feeding portion, not illustrated, configured to feed the sheet toward the image forming portion 40, and a fixing device 46 as a fixing portion configured to fix the toner image on the sheet. Note that examples of the sheet S used for image formation include plain paper, a synthetic resin sheet, cardboard, and an overhead projector sheet.

The image forming portion 40 includes a photosensitive drum 51 (51Y, 51M, 51C, 51K) and a rubber charging roller 52 (52Y, 52M, 52C, 52K) configured to charge the surface of the photosensitive drum 51. Further, a laser scanner unit 42 (42Y, 42M, 42C, 42K) and a developing device 20 (20Y, 20M, 20C, 20K) are provided. Also, a drum cleaner 55 (55Y, 55M, 55C, 55K), a pre-exposure device 54 (54Y, 54M, 54C, 54K), and an intermediate transfer unit 44 are provided.

The intermediate transfer unit 44 includes a primary transfer roller 47 (47Y, 47M, 47C, 47K), an intermediate transfer belt 50 (image bearing member), a secondary transfer roller 61, a secondary transfer counter roller 62, a tension roller 82, a driving roller 81, and a belt cleaner 80.

The photosensitive drum 51 (photosensitizer, photosensitive member) is a negatively charged organic photosensitizer (OPC) having an outer diameter of 30 mm. The photosensitive drum 51 has a three-layer structure in which an undercoat layer, a photocharge generation layer, and a charge transport layer are sequentially coated on an outer peripheral surface of an aluminum cylinder.

The developing device 20 includes an aluminum developing sleeve 24 (24Y, 24M, 24C, 24K). Inside the developing sleeve 24, a magnet roller, not illustrated, is included in a non-rotating state. The developing sleeve 24 bears a developer containing non-magnetic toner and a magnetic carrier and conveys the developer to a developing region at a position facing the photosensitive drum 51. Note that, when the developer in the developing device 20 decreases, an additional developer is supplied from toner bottle 41 (41Y, 41M, 41C, 41K) to the developing device 20.

The primary transfer roller 47 includes an elastic layer of ion conductive foamed rubber (NBR rubber) and a metal core, has an outer diameter of 15 to 20 mm, and has an electrical resistance of 1×10⁵ to 1×10⁸Ω (measurement environment: 23° C., 50% RH, applied voltage 2 kV).

The intermediate transfer belt 50 is stretched by a tension roller 82, a secondary transfer counter roller 62, and a driving roller 81 and rotates around the driving roller 81 as the driving roller 81 rotates. The tension roller 82 pushes the intermediate transfer belt 50 outward by a biasing force of a spring, not illustrated. Accordingly, a tension on the order of 2 to 5 kg is applied to the intermediate transfer belt 50.

The intermediate transfer belt 50 includes three layers: a base layer, an elastic layer, and a surface layer. In the present embodiment, the polyimide base layer has a thickness of 85 μm, the elastic layer made of CR rubber containing an ionic conductive agent and carbon black has a thickness of 260 μm, and the surface layer made of urethane containing PTFE has a thickness of 2 μm. The intermediate transfer belt 50 has an initial volume resistivity of 5×10⁹ Ω·cm and an MD1 hardness of 70 degrees.

Note that the base layer is made of a material containing an appropriate amount of carbon black as an antistatic agent in resins such as polyimide and polycarbonate or various rubbers, and has a thickness of 0.05 mm to 0.15 mm. The elastic layer is made of a material obtained by adding an appropriate amount of the ionic conductive agent to various rubbers such as urethane rubber and silicone rubber, and has a thickness of 0.1 mm to 0.500 mm in terms of followability to irregularity on the sheet S and durability of the sheet S. The surface layer is made of, for example, a single type of resin material such as polyurethane, polyester, and epoxy resin, or two or more types of elastic materials such as elastic material rubber, elastomer, butyl rubber, etc., as the base material, and the thickness is 0.0002 mm to 0.020 mm. In addition, in consideration of the transferability of the toner to the sheet S, for example, one or two, or more types of powders or particles such as a fluororesin or a material having a different particle size are dispersed in this base material as a material for improving the lubricity to form the surface layer.

The intermediate transfer belt 50 has a volume resistivity of 5×10⁸ to 1×10¹⁴ Ω·cm (measuring environment: 23° C., 50% RH) and a hardness of 60 to 85° in MD1 hardness (measuring environment: 23° C., 50% RH). The coefficient of static friction is 0.15 to 0.6 (measuring environment: 23° C., 50% RH, measuring instrument: type 94i manufactured by HEIDON).

The secondary transfer roller 61 is abutted and disposed on an outer peripheral surface of the intermediate transfer belt 50. The secondary transfer roller 61 includes a metal core and an elastic layer of ion conductive foamed rubber (NBR rubber), and is a roller having an outer diameter of 20 to 25 mm. The electrical resistance of the secondary transfer roller 61 is adjusted to 1×10⁵ to 1×10⁸Ω (N/N (23° C., 50% RH measurement), 2 kV applied).

Next, an image forming operation will be described. The image forming apparatus A is configured to be capable of executing a mode of forming a toner image of each color on each of the four photosensitive drums 51 to form a full color image, and a monochrome mode of forming a black toner image on the photosensitive drum 51K to form an image of a single black color. Hereinafter, a mode of forming a full-color image will be described.

First, when the controller 30 illustrated in FIG. 2 receives an image forming job signal, a sheet S is fed from a stack of sheets stored in a sheet cassette, not illustrated, by a feeding roller, not illustrated. Subsequently, the sheet S is conveyed by a registration roller 83 to a secondary transfer portion N formed by the secondary transfer roller 61 and the secondary transfer counter roller 62.

In contrast, in the image forming portion 40, first, a DC voltage is applied to the charging roller 52, so that the surface of the photosensitive drum 51 in contact with the charging roller 52 is charged. Subsequently, the laser scanner unit 42 irradiates the surface of the photosensitive drum 51 with a laser beam in accordance with an image signal transmitted from a host device such as an original reading device or a personal computer, not illustrated, or an external device such as a digital camera or a smartphone. Accordingly, an electrostatic latent image is formed on the surface of the photosensitive drum 51.

Subsequently, a DC voltage is applied to the developing sleeve 24 of the developing device 20, so that toner is attached to the electrostatic latent image formed on the surface of the photosensitive drum 51, so that a toner image is formed on the surface of the photosensitive drum 51. The toner image formed on the surface of the photosensitive drum 51 in this manner is sent to a primary transfer portion formed from the photosensitive drum 51 and the primary transfer roller 47.

A primary transfer voltage having a positive polarity opposite to a charging polarity of the toner is applied to the primary transfer roller 47, so that the toner image sent to the primary transfer portion is primarily transferred to the intermediate transfer belt 50. Accordingly, the toner images of the respective colors are sequentially superimposed on the intermediate transfer belt 50 to form a full-color toner image.

Subsequently, the toner image is sent to the secondary transfer portion N by a rotation of the intermediate transfer belt 50. Then, in the secondary transfer portion N, a secondary transfer voltage having a polarity opposite to the charging polarity of the toner and being controlled to a constant voltage is applied to the secondary transfer roller 61, so that the toner image on the intermediate transfer belt 50 is secondarily transferred to the sheet S.

In the present embodiment, constant voltage control is used to control the secondary transfer voltage, a DC voltage on the order of +1 kV to +7 kV is applied as the secondary transfer voltage, and a secondary transfer current on the order of +40 μA to +120 μA is passed. The metal core of the secondary transfer counter roller 45 a is connected to the ground potential. Note that in the present embodiment, a configuration is described in which a voltage is applied to the secondary transfer roller 45 b to perform secondary transfer, but a configuration in which a voltage is applied to the secondary transfer counter roller 45 a to perform the secondary transfer is also applicable.

The sheet S having the toner image transferred thereto is sent to the fixing device 46. Then, the toner image is fixed on the sheet S by being heated and pressurized by the fixing device 46. Subsequently, the sheet S is discharged to the outside of the image forming apparatus A.

Note that after the primary transfer of the toner image from the photosensitive drum 51 to the primary transfer roller 47, the surface of the photosensitive drum 51 is neutralized by the pre-exposure device 54. Subsequently, the toner remaining on the surface of the photosensitive drum 51 is scraped off and removed by the drum cleaner 55 configured to abut the photosensitive drum 51 with a predetermined pressing force. Further, the toner remaining on the intermediate transfer belt 50 after the secondary transfer is removed by the belt cleaner 80.

<Controller>

Next, an outline of the system configuration of the image forming apparatus A will be described.

FIG. 2 is a block diagram illustrating a part of the system configuration of the image forming apparatus A. As illustrated in FIG. 2, the image forming apparatus A includes a controller 30 having a CPU 31, a ROM 32, a RAM 33, and an input/output circuit 34.

The ROM 32 stores various data such as control programs and tables. The CPU 31 performs various types of arithmetic processing based on the control program and information stored in the ROM 32. The RAM 33 temporarily stores data.

That is, in the controller 30, the CPU 31 controls each device of the image forming apparatus A while using the RAM 33 as a work area based on the control program stored in the ROM 32. Then, the above-described image forming operation such as toner image formation on the photosensitive drum 51 is executed through the control of each device.

The input/output circuit 34 inputs and outputs a signal to and from the outside. The CPU 31 is connected to a sheet feeding portion, not illustrated, an image forming portion 40 and an operation portion 70, described later, via the input/output circuit 34 and performs control by exchanging signals with each portion.

An operation portion 70 is connected to the controller 30. The operation portion 70 is a touch panel member including operation buttons arranged on a screen of a liquid crystal panel. The user can perform various settings related to image formation and execute an image forming job by operating the operation portion 70. The controller 30 receives a signal from the operation portion 70 and operates various devices of the image forming apparatus A.

The controller 30 is connected to a temperature sensor 71 configured to detect an in-machine temperature and a humidity sensor 72 configured to detect the in-machine humidity. The temperature detected by the temperature sensor 71 and the humidity detected by the humidity sensor 72 are entered to the controller 30 as signals.

The controller 30 includes a charging power source 73 configured to apply a voltage to the charging roller 52, a developing power source 74 configured to apply a voltage to the developing sleeve 24, a primary transfer power source 75 configured to apply a voltage to the primary transfer roller 47, and a secondary transfer power source 76 configured to apply a voltage to the secondary transfer roller 61. The controller 30 controls these power supplies and applies a voltage to each member.

A voltage sensor 75 a and a current sensor 75 b are connected to the primary transfer power source 75. The voltage sensor 75 a detects the value of the voltage applied from the primary transfer power source 75 to the primary transfer roller 47. The current sensor 75 b detects the value of the primary transfer current that flows when a voltage is applied from the primary transfer power source 75 to the primary transfer roller 47. Note that four primary transfer power sources 75, four voltage sensors 75 a and four current sensors 75 b are provided corresponding to the four primary transfer rollers 47, respectively. The controller 30 can individually control these members.

Further, a voltage sensor 76 a and a current sensor 76 b are connected to the secondary transfer power source 76. The voltage sensor 76 a detects the value of the voltage applied from the secondary transfer power source 76 to the secondary transfer roller 61. The current sensor 76 b (current detecting unit) detects the value of the secondary transfer current that flows when a voltage is applied from the secondary transfer power source 76 to the secondary transfer roller 61.

<ATVC Control>

In the secondary transfer process, a current flow from the secondary transfer roller 61 to the secondary transfer counter roller 62 via the intermediate transfer belt 50. Here, as the image forming apparatus A is used, the electrical resistances of the secondary transfer roller 61, the intermediate transfer belt 50, and the secondary transfer counter roller 62 vary. For this reason, if it is desired to flow a desired secondary transfer current in the secondary transfer process, it is necessary to correct the value of the voltage applied to the secondary transfer roller 61 in accordance with variations in the electrical resistance.

Therefore, the image forming apparatus A performs ATVC control (another mode) that corrects the value of the secondary transfer voltage according to variations in electrical resistance of the secondary transfer roller 61, the intermediate transfer belt 50, and the secondary transfer counter roller 62. Hereinafter, the ATVC control will be described.

The ATVC control is performed during non-image formation. First, the controller 30 applies several types of voltages from the secondary transfer power source 76 to the secondary transfer roller 61. At this time, the voltage sensor 76 a detects several types of voltage values applied to the secondary transfer roller 61, respectively. The current sensor 76 b detects the value of the current that flows when several types of voltages are applied to the secondary transfer roller 61. Next, the controller 30 determines a value of the secondary transfer voltage Vb that allows a target current to be output in the secondary transfer process to flow based on the relationship between the values of several types of voltages applied to the secondary transfer roller 61 and the current values flowing at that time.

For example, first, a voltage ε1 is applied from the secondary transfer power source 76 to the secondary transfer roller 61, and the current ω1 flowing at that time is detected by the current sensor 76 b. If the current value detected by the current sensor 76 b is smaller than the target current value, the voltage ε2 larger than the voltage ε1 is next applied from the secondary transfer power source 76 to the secondary transfer roller 61, and the current ω2 flowing at that time is detected by the current sensor 76 b. Subsequently, the relationship between the voltage ε1 and the current ω1 and the relationship between the voltage ε2 and the current ω2 are linearly approximated to obtain the value of the secondary transfer voltage Vb that allows the target current to flow. Note that the types of voltages to be applied are not limited to two but may be three or more.

In the secondary transfer process, a secondary transfer current flows from the secondary transfer roller 61 to the secondary transfer counter roller 62 via the intermediate transfer belt 50 and the sheet S. For this reason, the impedance becomes higher by the amount of the sheet S than when ATVC control is executed. Therefore, at the secondary transfer voltage Vb determined by the ATVC control, a desired secondary transfer current cannot be passed, thereby resulting in a transfer failure.

Therefore, in consideration of the increase in impedance due to the sheet S, a divided voltage Vp of the sheet S, which is a voltage necessary for flowing a desired secondary transfer current, is applied in addition to the secondary transfer voltage Vb determined by ATVC control. That is, in the secondary transfer process, a voltage of Vb+Vp is applied as the secondary transfer voltage.

The ROM 32 stores a table, not illustrated, in which a type and a basis weight of the sheet S, a temperature and a humidity inside the image forming apparatus A, and a value of the divided voltage Vp of the sheet S are associated with each other. The controller 30 refers to the table, not illustrated, and determines the divided voltage Vp from the type and the basis weight of the sheet S selected by the user operating the operation portion 70 or a personal computer, and the temperature and humidity in the apparatus detected by the temperature sensor 71 and the humidity sensor 72.

<Setting Mode>

As described above, the value of the secondary transfer voltage is determined by ATVC control and the table, not illustrated. However, if the moisture content and electrical resistance of the sheet S used for image formation are significantly different from those of a standard sheet, the desired secondary transfer current does not flow at the value of the divided voltage Vp set in the table, not illustrated, which may result in a transfer failure. For example, if the moisture content of the sheet S used for image formation is significantly lower than that of a standard sheet, abnormal electric discharge may occur when secondary transfer is performed with the divided voltage Vp set in the table, not illustrated.

Therefore, the image forming apparatus A executes a setting mode for setting an appropriate secondary transfer voltage. In the setting mode, the image forming apparatus A adjusts the secondary transfer voltage in accordance with the type and the moisture content of the sheet S used for image formation. Hereinafter, this setting mode will be described with reference to the flowchart illustrated in FIG. 3.

As illustrated in FIG. 3, the user first operates the operation portion 70 (sheet setting portion) to select a sheet cassette, not illustrated, in which the sheet S used for image formation is stored (S1). Accordingly, the type and the size of the sheet S are specified. Here, the type and size of the sheet S accommodated in the sheet cassette can be stored and registered in the ROM 32 for each sheet cassette by the user operating the operation portion 70. In the present embodiment, as a registration method, three types of methods may be employed; a method of registering the sheet S according to the size and the basis weight such as A3 plain paper or A4 cardboard, a method of registering the sheet S by brand information, and a method of registering the sheet S by the user directly entering the size and the basis weight Note that a plurality of items of the brand information is registered in advance in the ROM 32, and the user selects a brand of the sheet S from the registered information. When the type and the size of the sheet S are designated, the appearance of the display screen of the operation portion 70 is as the screen illustrated in FIG. 4A (S2).

Next, on the screen illustrated in FIG. 4A of the operation portion 70, the user sets a secondary transfer voltage range for forming a patch image to be described later (S4). Specifically, the reference value (center value) of the secondary transfer voltage when a patch image is formed is set at ±20 levels. That is, the operation portion 70 is a voltage setting portion configured to set the value of the secondary transfer voltage when a patch image is formed. Here, if “0” is selected as the reference value, a value obtained by adding the secondary transfer voltage Vb set by the above-described ATVC control to the divided voltage Vp set in the table, not illustrated, stored in the ROM 32 about the sheet S is selected as a value for the secondary transfer voltage. That is, the ROM 32 stores data in which the type and size of the sheet S are associated with the reference value of the secondary transfer voltage when the patch image is formed in the setting mode. On the screen illustrated in FIG. 4A, the reference values stored in the ROM 32 associated with the type and size of the sheet S specified in step S1 are displayed by default. Note that when the image forming apparatus A is shipped, the reference value associated with all types and sizes of sheets S is “0”.

In the present embodiment, one level corresponds to 150 V. For this reason, for example, if “+1” is selected as the reference value, the voltage obtained by adding 150 V to the value of the divided voltage Vp set in the table, not illustrated, for the sheet S and the secondary transfer voltage Vb set by ATVC control corresponds to the reference value. That is, in the present embodiment, the reference value of the secondary transfer voltage when a patch image is formed can be set in the range of 3000 V. Note that the voltage value corresponding to one level and the number of levels that can be set are not limited to the numerical values described above and may be other numerical values.

Next, whether to perform the setting mode on one side or on both sides of the sheet S is set (S5). Subsequently, when the user presses the “output test page” button illustrated in FIG. 4A, the secondary transfer voltage is switched at ±5 level with respect to the reference value, and eleven patch images (test images) are transferred to the sheet S (S6). That is, the controller 30 transfers the plurality of patch images to the sheet S by switching the secondary transfer voltage to be applied to the secondary transfer roller 61 by 150 V (predetermined value) within a predetermined range centering on the reference value. That is, the controller 30 applies a plurality of different voltages to the secondary transfer roller 61 and outputs a plurality of patch images to be transferred when the plurality of voltages is applied. In this manner, a test chart that is the sheet S on which a plurality of patch images is formed is output.

For example, if a double-side coated sheet having a basis weight of 350 g/m² and an A3 size is selected as the sheet S to be used for image formation and the reference value is “0”, the reference secondary transfer voltage value is 2500 V. Therefore, eleven patch images are formed with the secondary transfer voltages switched from 1750 V to 3250 V by 150 V increments with reference to 2500 V.

Note that the lower limit value of the secondary transfer voltage level when a patch image is formed is “−20”, and the upper limit value is “+20”. For this reason, for example, even if “+17” is selected as the reference value, a patch image of a level higher than “+20” is not formed, and for the part exceeding “+20”, patch images of “+20” are repeatedly formed. That is, one patch images each from “+12” to “+19” are formed, and three patch images “+20” are formed.

FIG. 5A is a diagram illustrating a state in which a patch image is formed on a sheet S having a length of 420 to 487 mm in the conveyance direction. FIG. 5B is a diagram illustrating a state in which a patch image is formed on the sheet S having a length of 210 to 419 mm in the transport direction. As illustrated in FIGS. 5A and 5B, the level of the secondary transfer voltage is listed in the vicinity of each patch image. If eleven patch images do not fit on one sheet S, patch images are formed on two sheets S. Note that in the present embodiment, if patch images are formed on an A4 size sheet S, since eleven patch images cannot fit on two sheets S, 10 patch images are exceptionally formed on the sheet S.

Here, the size of the patch image needs to be a size that allows the user to easily determine the transferability. The transferability of a blue solid image and a black solid image is difficult to discriminate if the size of the patch image is small. Therefore, the size of the patch image is preferably 10 mm square or more, and more preferably 25 mm square or more.

Next, when the user selects the “OK” button illustrated in FIG. 4A, the screen illustrated in FIG. 4B is displayed. The user selects a patch image having the optimum transferability from the eleven patch images formed on the sheet S. Then, on the screen illustrated in FIG. 4B, the level of the secondary transfer voltage written together with the selected patch image is entered (S7, S8). That is, the operation portion 70 is a selecting portion configured to enter the selected patch image (selected image). Subsequently, when the user presses the “OK” button illustrated in FIG. 4B, the controller 30 sets the secondary transfer voltage corresponding to the selected level as the secondary transfer voltage to be applied during normal image formation and exits the setting mode (S9).

Here, the value of the secondary transfer voltage is increased stepwise from the smaller value, and a voltage at which the toner is transferred in a secondary color such as blue is a guideline for the lower limit value. Further, the voltage value is further increased from this lower limit value, and the voltage at which image defects occur in the black solid image and the halftone portion is a guideline for the upper limit value. When the user sets the level of the secondary transfer voltage within the range between the upper limit value and the lower limit value, desirable transferability is easily obtained.

If there is no patch image having optimum transferability among the eleven patch images formed on the sheet S, the process returns to step S4, and the user again selects the reference value of the secondary transfer voltage when the patch image is formed. Subsequently, a patch image is output in the same manner as described above, a patch image having an optimum transferability is selected, and a level is entered (S5 to S8). Subsequently, the “OK” button illustrated in FIG. 4B is selected and the controller 30 exits the setting mode (S9).

In this manner, in the setting mode, the controller 30 sets a voltage to be applied from the secondary transfer power source 76 to the secondary transfer roller 61 during image formation based on the voltage corresponding to the patch image selected by the user from the plurality of patch images transferred to the sheet S. Accordingly, even if the moisture content and electrical resistance of the sheet S used for image formation are greatly different from those of a standard sheet, desirable transferability can be ensured.

Here, if the type and the size of the sheet S specified in step S1 in the setting mode in the past and the type and size of the sheet S set in step S1 in the current setting mode are the same, the controller 30 performs the next control. That is, the secondary transfer voltage level set on the screen illustrated in FIG. 4B in the setting mode in the past is displayed on the screen illustrated in FIG. 4A as a default setting of a reference value of the secondary transfer voltage when a patch image is formed in the setting mode of this time (S2, S3). That is, the secondary transfer voltage to be applied during image formation set in the previous setting mode is set as a reference value (center value) of the secondary transfer voltage when a patch image is formed in the next setting mode. That is, every time the setting mode is performed, the CPU 31 rewrites the reference value of the secondary transfer voltage stored in the ROM 32 associated with the type and the size of the sheet S specified in step S1 to a level of the selected patch image in Step S8. From the next time onward, if the setting mode is executed for the sheet S, and on the screen illustrated in FIG. 4A, the reference value rewritten on the ROM 32 is displayed as a default setting.

Subsequently, the user sets the reference value of the secondary transfer voltage when forming the patch image in the same manner as described above (S4). That is, the user can change the reference value displayed as the default setting on the operation portion 70 to a different value by operating the operation portion 70. Note that the reference value displayed on the operation portion 70 as the default setting in the setting mode after being rewritten in the ROM 32 may be configured so that the user cannot change it.

In this manner, if the sheet S to which the patch image is transferred is the same in the setting mode in the past and the setting mode of this time, the controller 30 performs the following control. That is, based on the result of adjustment of the voltage applied to the secondary transfer roller 61 during image formation when the setting mode is performed in the past, the controller 30 changes the default setting of the reference value of the secondary transfer voltage displayed on the operation portion 70 when the patch image is formed in the setting mode of this time. In other words, the controller 30 is configured to preset a voltage value for setting a voltage to be applied when the patch images are transferred in the setting mode based on a voltage value, which is set in the previous setting mode. Accordingly, if the user wants to finely adjust the secondary transfer voltage in the situation in which the installation environment of the image forming apparatus A and the state of the sheet S are slightly changed, an optimum secondary voltage can be found easily without restarting the setting of the secondary transfer voltage from the beginning. For this reason, prolongation of execution time of the setting mode can be suppressed.

In other words, in the setting in which the setting of the secondary transfer voltage when the patch image is formed is initialized, the patch image may need to be formed again because the optimum secondary transfer voltage cannot be found when the patch image is formed. In contrast, by reflecting the result of the setting mode executed in the past as in the present embodiment, it is possible to suppress prolongation of execution time of the setting mode without repeating the formation of the patch image. Moreover, since the user can use the result of the setting mode in the past with the default setting without calling the result of the setting mode in the past, the result of the setting mode in the past can be easily used, and the usability can be improved.

Second Embodiment

Next, a second embodiment of the image forming apparatus A according to the present invention will be described. Parts that are the same as those in the first embodiment are not described specifically by using the same drawings and denoting the same reference numerals.

In the first embodiment, the controller 30 makes the operation portion 70 display the secondary transfer voltage corresponding to the patch image selected in the setting mode in the past as is as the level of the reference value of the secondary transfer voltage during patch image formation in the setting mode of the next time. In contrast, in the present embodiment, the controller 30 makes the operation portion 70 display a level corresponding to 80% of the secondary transfer voltage corresponding to the patch image selected in the setting mode in the past as the level of the reference value of the secondary transfer voltage during patch image formation in the setting mode of the next time.

For example, the level of the secondary transfer voltage corresponding to the patch image selected in the previous setting mode is assumed to be “+15”. In this case, the controller 30 causes “+12” to be displayed as a default setting as a level of the reference value of the secondary transfer voltage to be set when the patch image is formed on the screen illustrated in FIG. 4A in the setting mode for the next time.

The reason is as follows. That is, the cause of occurrence of the secondary transfer failure often includes various factors in addition to variations in installation environment of the image forming apparatus A and variations in state of the sheet S. For this reason, an optimum secondary transfer voltage is not always found by forming a patch image based on the secondary transfer voltage set in the setting mode of the previous time. That is, an optimum secondary transfer voltage may be found within the limited number of patch images by suppressing the value of the secondary transfer voltage value to be reflected.

Third Embodiment

Next, a third embodiment of the image forming apparatus A according to the invention will be described. Parts that are the same as those in the first and second embodiments are not described specifically by using the same drawings and denoting the same reference numerals.

FIG. 6 is a schematic cross-sectional view of the image forming apparatus A according to the present embodiment. As illustrated in FIG. 6, in the image forming apparatus A of the present embodiment, an in-line spectroscopic sensor 90 configured to detect a patch image is provided at a position downstream of the fixing device 46 in the sheet conveying direction. Other mechanical configurations are the same as those of the first embodiment.

FIG. 7 is a schematic diagram of the spectroscopic sensor 90. As illustrated in FIG. 7, the spectroscopic sensor 90 includes a white LED 201 that irradiates light to the patch image T formed on the sheet S, and a diffraction grating 202 that disperses the reflected light reflected from the patch image T for each wavelength. Further, the spectroscopic sensor 90 also includes the lens 206 configured to collect the light irradiated from the white LED 201 on the patch image T and collect the light reflected from the patch image T on the diffraction grating 202.

Further, the spectroscopic sensor 90 includes a line sensor 203 including a plurality of pixels that detects light separated for each wavelength by the diffraction grating 202. The light intensity value of each pixel detected by the line sensor 203 is entered to the CPU 31 and subjected to various types of calculation and stored in the ROM 32.

Four spectroscopic sensors 90 are arranged in the sheet width direction orthogonal to the conveyance direction of the sheet S. These four spectroscopic sensors 90 individually detect a plurality of patch images formed at different positions in the sheet width direction. Note that the four spectroscopic sensors 90 may be used in such a manner that one patch image is detected by some of the four spectroscopic sensors 90, and the results of detection are averaged.

The results of detection of the patch image performed by the spectroscopic sensors 90 are entered to the CPU 31 as spectral reflectance data, and a density calculation is performed in the CPU 31. In a conversion calculation from spectral reflectance data to density value, a status A filter illustrated in FIG. 8A is used for yellow, magenta, and cyan patch images for the obtained spectral reflectance for each wavelength. The visual spectral characteristic (Visual) illustrated in FIG. 8B are used for the black patch image. The status A filter and the visual spectral characteristics are stored in the memory 31.

Further, the CPU 31 calculates a Lab value (chromaticity value) defined by the CIE (International Commission on Illumination) based on the spectral reflectance. The Lab values are calculated using a calculation method specified in ISO13655, with reference to the color matching functions x(λ), y(λ), z(λ) specified in JIS Z8701, and the standard light spectral distribution SD50(λ) specified in JIS Z8720.

Note that as a calibration process for the spectroscopic sensor 90, white LED light quantity adjustment using a white reference plate is performed to correct the reference spectral reflectance. For this calibration process, a known process can be arbitrarily used.

<Setting Mode>

Next, a setting mode using the spectroscopic sensor 90 according to the present embodiment will be described using a flowchart illustrated in FIG. 9. Note that in the following description, steps of performing the same processes as those described with reference to FIG. 3 in the first embodiment are denoted by the same reference numerals, and description thereof is simplified.

As illustrated in FIG. 9, the user first operates the operation portion 70 to select a sheet cassette, not illustrated, in which the sheet S used for image formation is stored (S1). Next, if the type and the size of the specified sheet S are the same as those at the time of execution of the setting mode in the past, the level of the secondary transfer voltage set in the setting mode in the past is displayed as a default setting of a reference value of the secondary transfer voltage when a patch image is formed in the setting mode of this time (S2, S3).

Next, when the patch image is formed, the user sets the reference value (center value) of the secondary transfer voltage and whether to implement the setting mode one side or both sides of the sheet S. (S4, S5). Next, when the user presses the “output test page” button illustrated in FIG. 4A, the secondary transfer voltage is switched at ±5 level with respect to the reference value, and eleven patch images are transferred to the sheet S (S6).

Next, the patch image formed on the sheet S is detected by the spectroscopic sensor 90 (S101). The spectroscopic sensor 90 outputs spectral reflectance data of each patch image to the controller 30. The controller 30 converts the spectral reflectance of the black and gray (halftone) patch image into a density value, and converts the spectral reflectance of the blue patch image into a Lab value. Subsequently, the controller 30 selects a patch image in which these density value and the Lab value are predetermined values stored in the ROM 31 in advance, and automatically enter the level corresponding to the patch image as a level of the secondary transfer voltage on the screen illustrated in FIG. 4B (S102). That is, the controller 30 causes the voltage applied to the secondary transfer roller 61 during image formation determined based on the result of detection performed by the spectroscopic sensor 90 to be displayed on the screen of the operation portion 70 as a default setting.

Note that if the density value and Lab value converted from the spectral reflectance of the patch image are not the predetermined preset in the ROM 32, the controller 30 selects the patch image having the density value and Lab value closest to the predetermined values. However, in such a case, the patch image may be formed again by changing the reference value of the secondary transfer voltage as in step S7 of the first embodiment.

Next, on the screen illustrated in FIG. 4B, the user confirms the level of the automatically entered secondary transfer voltage and presses the “OK” button if there is no problem. If the user wants to change the level of the secondary transfer voltage, it is achieved by manually entering the level and pressing the “OK” button. Accordingly, the controller 30 sets the secondary transfer voltage corresponding to the selected level as the secondary transfer voltage to be applied during normal image formation and exits the setting mode (S9). Note that the controller 30 may be configured not to display such a confirmation screen but to set a voltage to be applied to the secondary transfer roller 61 during image formation based on the result of detection performed by the spectroscopic sensor 90.

In this manner, in the present embodiment, the patch image is detected by the spectroscopic sensor 90, and the controller 30 selects and automatically enters the patch image according to the result of detection. Accordingly, the process of comparing patch images by the user is omitted or simplified, and the setting of the secondary transfer voltage can be simplified.

Note that in the present embodiment, the controller 30 calculates the density value and Lab value of the patch image based on the spectral reflectance data output from the spectroscopic sensor 90 and selects the patch image having the optimum transferability based on these values. However, the present invention is not limited thereto, and for example, the same effect as described above can be achieved even with a configuration in which the color difference V between the sheet S and the patch image is obtained using the spectroscopic sensor 90 and the patch image is selected based on the color difference V.

Here, the color difference V is a distance between two points in a three-dimensional space of the Lab and is calculated by the following equation 1. V=((L element of sheet S−L element of patch image T)²+(a element of sheet S−a element of patch image T)²+(b element of sheet S−b element of patch image T)²)^(0.2)  (1)

In the present embodiment, although the spectroscopic sensor 90 is used as the image detecting unit configured to detect the patch image, a CIS type or CCD type image sensor (optical sensor) may be used instead of the spectroscopic sensor 90. In this case, the image sensor detects the light intensity through filters corresponding to red, green, and blue, and the controller 30 calculates the light intensity by converting it into a density value. The controller 30 selects a patch image in which the density value is predetermined value stored in the ROM 32 in advance, and automatically enters the level of the secondary transfer voltage corresponding to the patch image as a level of the secondary transfer voltage on the screen illustrated in FIG. 4B.

In the present embodiment, although the spectroscopic sensor 90 is disposed on the conveyance path of the sheet S, the present invention is not limited thereto. That is, for example, the spectroscopic sensor 90 may be arranged on the upper part of the main body of the image forming apparatus A, and the sheet S on which the patch image is formed may be placed on the spectroscopic sensor 90 and scanned by a user.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

This application claims the benefit of Japanese Patent Application No. 2019-012271, filed Jan. 28, 2019, which is hereby incorporated by reference herein in its entirety. 

What is claimed is:
 1. An image forming apparatus comprising: an image bearing member; a transfer member configured to transfer a toner image carried on the image bearing member to a sheet by being applied with a voltage; a controller configured to execute a mode of outputting a test chart, which is formed by transferring a plurality of test toner images from the image bearing member, to the sheet, for adjusting a transfer voltage to be applied to the transfer member during image formation, the plurality of test toner images being formed by applying a plurality of different voltages to the transfer member, the plurality of different voltages including a reference voltage, a plurality of first test voltages set in conjunction with the reference voltage and having a voltage level lower than the reference voltage, and a plurality of second test voltages set in conjunction with the reference voltage and having a voltage level higher than the reference voltage; and an operation portion configured to input a type of a sheet on which the mode is executed and configured to input a reference value for changing the reference voltage, wherein in a case the type of the sheet inputted in a previous execution of the mode and the type of the sheet inputted in a next execution of the mode are the same, the controller is configured to set the reference voltage in the next execution of the mode on the basis of the reference voltage which is changed via the operation portion in the previous execution of the mode.
 2. The image forming apparatus according to claim 1, wherein the reference voltage to be set in the next execution of the mode can be changed via the operation portion.
 3. The image forming apparatus according to claim 1, further comprising an image detecting unit configured to detect information relating to a density of the test images, wherein the controller sets the transfer voltage to be applied to the transfer member during image formation based on a result of detection detected by the image detecting unit.
 4. The image forming apparatus according to claim 3, wherein the image detecting unit outputs data relating to spectral reflectance of the test images based on reflected light reflected from the test images, and the controller sets a voltage to be applied to the transfer member during image formation based on the data.
 5. The image forming apparatus according to claim 3, wherein the image detecting unit is an optical sensor.
 6. The image forming apparatus according to claim 1, further comprising a current detecting unit configured to detect a value of a current that flows when a voltage is applied to the transfer member, wherein the controller can execute another mode for setting a voltage to be applied to the transfer member during image formation based on a relationship between a voltage applied to the transfer member during non-image formation and a current detected by the current detecting unit at that time, and wherein the controller sets the reference voltage based on the reference value set in the mode and the relationship.
 7. The image forming apparatus according to claim 1, wherein the image bearing member is an intermediate transfer belt onto which a toner image formed on a photosensitive member is transferred.
 8. An image forming apparatus comprising: an image bearing member; a transfer member configured to transfer a toner image carried on the image bearing member to a sheet by being applied with a voltage; a controller configured to execute a mode of outputting a test chart, which is formed by transferring a plurality of test toner images from the image bearing member, to the sheet, for adjusting a transfer voltage to be applied to the transfer member during image formation, the plurality of test toner images being formed by applying a plurality of different test voltages to the transfer member, the plurality of different test voltages including a reference voltage, a plurality of first test voltages set in conjunction with the reference voltage and having a voltage level lower than the reference voltage, and a plurality of second test voltages set in conjunction with the reference voltage and having a voltage level higher than the reference voltage; and an operation portion configured to input a type of a sheet on which the mode is executed, wherein after outputting the test chart in the mode, the controller is configured to adjust the transfer voltage applied to the transfer member during image formation based on the test voltage corresponding to the plurality of test toner images selected from the operation portion, and wherein in a case the type of the sheet inputted from the operation portion in a previous execution of the mode and the type of the sheet inputted from the operation portion in a next execution of the mode are the same, the controller is configured to set the reference voltage in the next execution of the mode based on the transfer voltage adjusted in the previous execution of the mode.
 9. The image forming apparatus according to claim 8, wherein in the case the type of the sheet inputted from the operation portion in the previous execution of the mode and the type of the sheet inputted from the operation portion in the next execution of the mode are the same, the controller is configured to set the reference voltage in the next execution of the mode based on a level of the transfer voltage adjusted in the previous execution of the mode relative to the reference voltage set in the previous execution of the mode.
 10. The image forming apparatus according to claim 8, wherein the reference voltage to be applied in the next execution of the mode can be changed via the operation portion.
 11. The image forming apparatus according to claim 8, further comprising a current detecting unit configured to detect a value of a current that flows when a voltage is applied to the transfer member, wherein the controller can execute another mode for setting the transfer voltage to be applied to the transfer member during image formation based on a relationship between a voltage applied to the transfer member during non-image formation and a current detected by the current detecting unit at that time, and wherein the controller is configured to set the reference voltage to be set in the next execution of the mode based on the reference voltage set in the previous execution of the mode, the transfer voltage adjusted in the previous execution of the mode, and the relationship.
 12. An image forming apparatus comprising: an image bearing member; a transfer member configured to transfer a toner image carried on the image bearing member to a sheet by being applied with a voltage; an image detecting unit configured to detect information relating to a density of test images; a controller configured to execute a mode of outputting a test chart, which is formed by transferring a plurality of test toner images from the image bearing member, to the sheet, for adjusting a transfer voltage to be applied to the transfer member during image formation, the plurality of test toner images being formed by applying a plurality of different voltages to the transfer member, the plurality of different test voltages including a reference voltage, a plurality of first test voltages set in conjunction with the reference voltage and having a voltage level lower than the reference voltage, and a plurality of second test voltages set in conjunction with the reference voltage and having a voltage level higher than the reference voltage; and an operation portion configured to input a type of a sheet on which the mode is executed, wherein the controller is configured to adjust the transfer voltage to be applied to the transfer member during image formation based on a detection result of the test images detected by the image detecting unit in the mode, and wherein in the case the type of the sheet inputted from the operation portion in a previous execution of the mode and the type of the sheet inputted from the operation portion in a next execution of the mode are the same, the controller is configured to set the reference voltage in the next execution of the mode based on the transfer voltage adjusted in the previous execution of the mode.
 13. The image forming apparatus according to claim 12 , wherein in the case the type of the sheet inputted from the operation portion in the previous execution of the mode and the type of the sheet inputted from the operation portion in the next execution of the mode are the same, the controller is configured to set the reference voltage in the next execution of the mode based on a level of the transfer voltage adjusted in the previous execution of the mode relative to the reference voltage set in the previous execution of the mode.
 14. The image forming apparatus according to claim 12, wherein the reference voltage to be applied in the next execution of the mode can be changed via the operation portion.
 15. The image forming apparatus according to claim 12, further comprising a current detecting unit configured to detect a value of a current that flows when a voltage is applied to the transfer member, wherein the controller can execute another mode for setting a voltage to be applied to the transfer member during image formation based on a relationship between a voltage applied to the transfer member during non-image formation and a current detected by the current detecting unit at that time, and wherein the controller is configured to set the reference voltage in the next execution of the mode based on the reference voltage set in the previous execution of the mode, the transfer voltage adjusted in the previous execution of the mode, and the relationship.
 16. An image forming apparatus comprising: an image bearing member; a transfer member configured to transfer a toner image carried on the image bearing member to a sheet by being applied with a voltage; controller configured to execute a mode of outputting a test chart, which is formed by transferring a plurality of test toner images from the image bearing member, to the sheet, for adjusting a transfer voltage to be applied to the transfer member during image formation, the plurality of test toner images being formed by applying a plurality of different test voltages to the transfer member, the plurality of different test voltages including a reference voltage, a plurality of first test voltages set in conjunction with the reference voltage and having a voltage level lower than the reference voltage, and a plurality of second test voltages set in conjunction with the reference voltage and having a voltage level higher than the reference voltage; and an operation portion configured to input a type of a sheet on which the mode is executed, wherein the operation portion is configured to input a reference value for changing the reference voltage. 